Digital Logic Fundamentals Unit 7 – Tri-State Output
UNIT 7 – TRI-STATE OUTPUT
UNIT OBJECTIVE
At the completion of this unit, you will be able to demonstrate the operation of a tri-state buffer
by using the TRI-STATE OUTPUT circuit block on the DIGITAL LOGIC FUNDAMENTALS
circuit board.
UNIT FUNDAMENTALS
Tri-state logic devices have three distinct out-put states. In addition to the high (logic 1) and low
(logic 0) output states, tri-state devices have a third output state called the high-impedance state,
or high-Z state. The high-Z state is equivalent to an open circuit at the output of the device; the
output is in a floating condition.
This is the schematic symbol for a tri-state buffer.
A logic 1 at the EN INPUT permits the buffer to operate normally: the output is the same logic
state as the input.